1. Technical Field
The present invention relates to a method of judging whether or not darkness of a foreign matter has been read at the time of reading the darkness of a test pattern, a method of calculating a representative value of darkness of a test pattern, and an apparatus that judges whether or not darkness of a foreign matter has been read.
2. Related Art
Among printing apparatuses such as inkjet printers are those that, for example, adjust unevenness in ink ejection by reading, with a scanner etc., the darkness of a test pattern printed using the printing apparatus targeted for adjustment. (See, for example, JP-A-2-54676.)
However, there is a possibility that a foreign matter, such as dust and dirt, may be adhering to the surface of the test pattern or the reading mechanism of the scanner, and, at the time of reading the test pattern darkness, the darkness of the foreign matter may also be read. In such cases, if the darkness of the foreign matter is used for the above-mentioned adjustment processing, the adjustment precision will be affected by the darkness of the foreign matter.
Therefore, it is desirable to judge whether or not the darkness of a foreign matter has been read at the time of reading the darkness of the test pattern. A conceivable example of a judgment method, which may be employed particularly in cases where the test pattern is printed with predetermined darkness, is to “compare, with a predetermined threshold, the difference between the maximum value and the minimum value of readout values on the darkness of the test pattern, and judge that the darkness of a foreign matter has been read if the difference is larger than the threshold”.
With this method, however, the judgment is made based merely on the difference between the maximum value and the minimum value. Therefore, the presence of extremely small dirt which would hardly affect the above-mentioned adjustment may fall under the above-mentioned judgment condition. That is, the presence of dirt whose planar dimension is small enough as not to cause any substantial problem may be judged that the darkness of a foreign matter has been read, and as a result thereof, a worker carrying out the adjustment task may be forced to perform cleaning and other unnecessary removal tasks even in the case of extremely small dirt. Therefore, the above-mentioned method has a drawback in terms of judgment accuracy.